The invention relates to an apparatus for the fine blanking of workpieces from a material, comprising a press plate, which is under the pressure of a V-ring cylinder and has a V-ring, and a blanking punch which is guided in the press plate and to which a die plate with counterholder (ejector) is assigned at a ram.
The working principle of fine blanking is shown and described in “Feinschneiden”, Handbuch für die Praxis, publisher Feintool AG Lyss, 2nd edition, 1977, pages 15 to 17. A fine-blanking tool essentially comprises a press plate with V-ring, in which a blanking punch is guided. A counterholder or ejector in a die plate is assigned to the blanking punch in a position opposite the latter.
A workpiece, for example a metal sheet, is inserted between press plate and blanking punch or die plate and counterholder. The top part and the bottom part of the tool are closed and the workpiece is clamped in position inside and outside the cutting line by means of a V-ring force and a counterforce. The press plate and the die plate are guided relative to the blanking punch and counterholder and thus the workpiece is cut out of the material. After the workpiece has been cut out, the tool is opened and the workpiece is usually ejected from the die plate by means of the counterholder.
In these conventional fine-blanking presses, the force of the V-ring cylinder, which is usually arranged in the top crosshead of the machine column, opposes the blanking force. The counterholder cylinder, which is integrated in the ram or in the working piston, also presses the workpiece against the top part of the tool; the counterholder supporting force likewise opposes the blanking force. The counterforce of the V-ring cylinder may be up to 50% and that of the counterholder up to 25% of the working force. However, this considerably reduces the capacity of the entire apparatus.
To solve this problem, DE 196 42 635 A1 proposes that V-ring cylinder and counterholder cylinder be arranged in a different way, the V-ring cylinder being integrated in a separate crosspiece above the column and being connected to the ram via pillars, so that it moves upward in synchronism with the ram. The counterholder cylinder is in turn arranged between the ram and a bottom crosshead of the column, no relative movement taking place between counterholder cylinder and column during stroke, so that the supporting forces of the counterholder cylinder are absorbed by the machine column.
Apart from the fact that this apparatus is of very complicated construction and has to work with various hydraulic operating circuits, it has been found that, for strength reasons, the crosspiece for the V-ring cylinder has to be of very solid construction. This in turn requires a configuration as a heavy and expensive machine, so that the energy saving due to the traveling V-ring cylinder is nullified by this large mass to be moved during each stroke. In addition, assembly is very difficult.